High rates of heterosexual transmission of HIV have been observed in Haiti and some developing countries. Counseling with provision of condoms has not significantly altered behavior or HIV transmission. HIV vaccines may be the best strategy for interruption of transmission. The advances in vaccines research and the results of phase I/II clinical trials have led to the recognition that the infrastructure must be established for HIV vaccine efficacy trials. Cornell University Medical College maintains a research unit in Haiti for the study and control of infectious diseases. Since 1980 this unit has conducted studies of infantile diarrhea, typhoid fever, sexually transmitted diseases, leprosy, tuberculosis, and particularly HIV infection and AIDS. During these twelve years an infrastructure has been developed that will be strengthened and adapted for the major efficacy trials anticipated by the NIAID/PAVE program. This proposal is further strengthened by the collaboration with the Vaccine Evaluation Units at Vanderbilt University. This PAVE proposal aims to: 1) define the incidence of HIV infection in the mothers of infants admitted to the Cornell infantile diarrhea/rehydration unit (CIDRU) and the male sex partners of these women, 2) define the incidence of co-factors associated with HIV transmission and other sexually transmitted diseases in this population, 3) supply 50 or more viral isolates for genetic and antigenic variation studies. In addition, special emphasis will be placed on obtaining isolates from both members of seroconverting discordant couples and from infected mother-infant pairs for determination of genetic and antigenic characteristics of the transmitted strains, 4) continue training of Haitian personnel in technologies related to the preparation and conduct of a HIV vaccine clinical trial, 5) strengthen and expand the core services such as administration, laboratory and data management for studies of HIV transmission and preparation for HIV vaccine trials in Haiti, 6) determine through the administration of hepatitis B and Hemophilus influenzae type b vaccine, the seroprevalence of hepatitis B, the efficacy of hepatitis B vaccine, and the acquisition of hemophilus anti-PRP antibodies after vaccine and natural infection. This PAVE will provide the necessary information on HIV rates and co-factors for HIV transmission, as well as genetic and antigenic determinants, and prepare the investigators for many of the logistical challenges inherent in testing an AIDS vaccine.